I. Field of the Invention
This invention relates to a process for the production of jet fuels, diesel fuels, multi-purpose fuels meeting the critical properties required for both high grade jet fuels and diesel fuels, and high quality blending components useful for the production of such fuels.
II. Description of the Prior Art
Various fractions and blends of mid-distillate fuels are required for the operation and functioning of both diesel and jet engines. The diesel engine, a consumer of mid-distillate fuels, is one of the world's most efficient power sources. It converts more of the energy contained in a given quantity of fuel into useful energy than any other power-developing engine. The future of the diesel engine, because of its ability to burn mid-distillate fuels at higher efficiency over the entire range of speed and load is assured. There are strong incentives for the continued development of railroad, marine, and automotive diesel engines for both commercial and military use. Moreover, the development of advanced jet engines for military and commercial aviation use advances rapidly. Consequently, the growth in the demand for mid-distillate fuels is expected to continue.
Early British and American jet engines were developed on a kerosene fuel similar in many respects to JP-5, a 320.degree.-520.degree. F. boiling range fuel having a freeze point of -50.degree. F. The U.S. military version of this fuel was called JP-1, and the specifications for this fuel also required a freeze point of -50.degree. F. Because such narrow-cut kerosene was of limited availability, the U.S. Air Force adopted as its standard a wide cut mixture of gasoline and kerosene capable of being produced in high yield from petroleum crude.
The first wide cut-military fuel, JP-3, had the vapor pressure characteristics of aviation gasoline. This degree of volatility, however, proved excessive in actual use and accordingly the front end boiling range of the fuel was adjusted to a maximum vapor pressure of 3 psi. The result was JP-4, the standard workhorse fuel for most of the world's air forces. JP-4 is a fuel having a 100.degree.-550.degree. F. boiling range, and a freeze point of -76.degree. F. The U.S. Navy, however, requires the use of JP-5 kerosene fuel because high flash products are necessary to insure safety aboard aircraft carriers. AVTUR, a kerosene fuel first used by the Royal Air Force and still in use, became the model for the first commercial jet fuels principally because British Airline launched the jet age, first with the Comet 1 and then with the turboprop Viscounts. An American version of AVTUR followed which was called Jet A. This being followed by a commercial version of JP-4 which was called Jet B, or Kerosene 1B.
Diesel fuels are primarily used by the military as transportation, or automotive fuels. Diesel fuel has a boiling range of about 320.degree.-650.degree. F., and a pour point of 0.degree. F. Typically, diesel fuel is constituted of a 40% admixture of a 320.degree.-550.degree. F. kerosene and 60% light cat cycle oil fractions. A special diesel fuel known as "Artic Diesel," largely used by the military, is constituted of a 200.degree.-520.degree. F. naphtha/kerosene cut having a pour point of -40.degree. F.
Various engine factors are significant for the proper performance of jet and diesel engines, and consequently certain fuel quality standards are necessary for maintaining acceptable engine performance. Certain of these properties are particularly critical. For example, in jet fuels low freeze points are required to maintain fluidity, or flowability of the fuel at low temperatures. Flash points must be relatively high, since volatile materials are more readily ignitable in the event of spills. A consideration of the flash point of a jet fuel is thus invariably an important safety factor in determining the use of a particular jet fuel for a given use. Thus, the reason for the U.S. Navy's insistance on the use of JP-5 aboard carrier aircraft is because of the fire hazard of spills. Thermal stability is also an important consideration because, under certain temperature conditions some fuels can form insoluble deposits or varnish to clog screens and fine nozzle ports which reduces fuel flow to the engine, or impair the heat exchange characteristics of the fuel. The levels of aromatics and olefins in a jet fuel are also limited to certain specifications. Diesel fuels, on the other hand, are governed by criteria which may or may not be closely related to those governing the requirements of jet fuels. For example, with the exception of Artic Diesel, which is used in extremely cold climates, freeze point is not an important consideration in determining the standards of a fuel for use in diesel engines. However, flash point, an index of the fire hazard, is of considerable importance, albeit this property is of far lesser importance for use in an automotive diesel engine as compared with its use in a high performance jet engine. Pour point, or the minimum temperature at which a fuel will remain liquid, and flash point are particularly important considerations in all diesel fuels. Operation below the cloud point, or temperature at which crystals begins to form, will result in the pluggage of the fuel filters by wax.
There are similarities, but also wide differences between the characteristics required for a jet fuel vis-a-vis the characteristics required for a diesel fuel. Moreover, there are considerable differences between the characteristics of one jet fuel and another, and between the characteristics of one diesel fuel and another. Thus, jet fuels must be tailored for a wide variety of engines, and types of aircraft. A consideration of the best jet fuel for a specific use would thus be determined by the type of engine, e.g., whether the engine is a turbo jet, a turboprop, a turbofan, or ramjet engine, and the type of airplane, or service in which the airplane is to be used. A fuel best suited for a Mock 1 aircraft may not be suited for use in a Mock 3 airplane. Military usage may dictate the use of different fuels from those used commercially. Further, as suggested, there are differences between the characteristics of one diesel fuel and another. For example, a diesel fuel used for personal automative transportation purposes in Texas would differ considerably from an artic diesel, or diesel manufactured for use in an artic climate. Also, certain types of diesel engines are more critical of fuel than others. For example, high speed engines (1000-2500 RPM) require a higher quality fuel than medium speed engines (500-1000 RPM), which in turn are more critical of fuel than low speed engines (under 500 RPM). The standardization of materials, or parts, is always a highly desirable objective, particularly among the military. This however, is often an illusory objective, particularly with fuels because of the wide range of requirements dictated by the varying usages of one jet fuel and another, or between one diesel fuel and another, or by the varying usages required of jet fuels and diesel fuels, supra.
There is, in any event, a need for a novel process for the production in good yields of jet fuels and diesel fuels, particularly high quality jet fuels and diesel fuels. There is also a need for a process suitable for the production of standard fuels, or fuels suitable for a wide number of commercial and military needs, notably multi-purpose jet fuels or multi-purpose diesel fuels, or multi-purpose fuels suitable for use in both jet and diesel engines; as well as a need for such fuel compositions.
It is, accordingly, a primary objective of this invention to fill these and other needs.
A specific object of this invention is to provide a process suitable for the production of standard fuels, or fuels suitable for a wide number of commercial and military needs, notably multi-purpose jet fuels or multi-purpose diesel fuels, multi-purpose fuels suitable for use as both a jet fuel and diesel fuel, or high quality blending component for the production of such fuels.
A further, and equally specific object of this invention is to provide multi-purpose jet fuels or multi-purpose diesel fuels, multi-purpose fuels suitable for use as both a jet fuel and diesel fuel, or high quality blending component suitable for the production such fuels.
A further object is to provide multi-purpose fuel compositions, and process for the production of multi-purpose fuel compositions which meet at least the minimum requirements of both jet and diesel fuels as relates to such cold flow properties as freeze point and pour point, flash point, thermal stability, and aromatics and olefins concentrations; as well as imposing limitations on the concentrations of 450.degree. F..sup.+ n-paraffins levels in such compositions.